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Acta Polytechnica Vol. 52 No. 3/2012

Effect of Gas Mixture Composition on the Parameters of an

Internal Combustion Engine

Andrej Chŕıbik1, Marián Polóni1, Ján Lach1

1
Slovak University of Technology in Bratislava, Faculty of Mechanical Engineering, Institute of Transport Technology
and Engineering Design, Department of Automobiles, Ships and Combustion Engines,
Námestie slobody 17, 812 31 Bratislava, Slovak Republic

Correspondence to: andrej.chribik@stuba.sk

Abstract

This paper deals with the use of the internal combustion piston engine, which is a drive unit for micro-cogeneration

units. The introduction is a brief statement of the nature of gas mixture compositions that are useful for the purposes of

combustion engines, together with the basic physical and chemical properties relevant to the burning of this gas mixture.

Specifically, we will discuss low-energy gases (syngases) and mixtures of natural gas with hydrogen. The second section

describes the conversion of the Lombardini LGW 702 combustion engine that is necessary for these types of combustion

gases. Before the experimental measurements, a simulation in the Lotus Engine simulation program was carried out to

make a preliminary assessment of the impact on the performance of an internal combustion engine. The last section of

the paper presents the experimental results of partial measurements of the performance and emission parameters of an

internal combustion engine powered by alternative fuels.

Keywords: natural gas, hydrogen, synthesis gas, engine parameters.

1 Introduction

In the current development of combustion engines,
there is a trend to put emphasis not only on perfor-
mance and cost parameters, but also on environmen-
tal parameters, the aim being to achieve the most
acceptable values. The spotlight is also therefore on
non-traditional power sources. One of these energy
carriers is hydrogen.

A mixture of natural gas and hydrogen will above
all be used to drive vehicles in urban areas, where
there are higher requirements on complying with
emission regulations. This mixture combines the ad-
vantages of the individual components of the mixture.
The current natural gas (H2NG0) is made up mainly
of methane (97 % vol.), and has a calorific value of
50 MJ·kg−1 and an octane number of 130. A combi-
nation of this natural gas with oxygen to power inter-
nal combustion engines can achieve multiple benefits
in terms of combustion and emissions:
– Limited flammability – as the proportion of hy-
drogen in the mixture with natural gas increases,
the flammability range also increases. A mixture
that contains 30 % of hydrogen has the theoret-
ical flammability range limit λ = (2.67 to 0.52),
while when natural gas is burned λ = (1.92 to
0.57).

– Ignition delay time – adding hydrogen to natural
gas reduces the delay time of ignition, and in the

case of a 5 % proportion of hydrogen the delay
time is reduced to about one half of the delay
when an internal combustion engine operates on
natural gas.

– Burning rate – increasing the proportion of hy-
drogen in the gas mixture increases the flame
speed, and hence the time of burning the mix-
ture itself, resulting in faster heat release.

– Emissions – there is some reduction in the con-
tent of carbon (CO2, CO, CHx), since the addi-
tion of hydrogen increases the H/C ratio. How-
ever, the addition of hydrogen increases the
amount of NOx, because there is an increase in
the combustion temperature.

The second fuel types that will be used for power-
ing internal combustion engines in cogeneration units
are called synthesis gases. These gases are derived
mainly by gasification of wastes. The fuel composi-
tion depends on the gasifier that is used, and on the
type of waste. Synthesis gases can be divided into two
basic groups. The first group is synthesis gas with a
30 % proportion of inert gases, and the second group
is synthesis gas with a 60% proportion of inert gases.
The first group is characterized as fuel SYNGAS 1,
with the following composition — (CH4 – 15 % H2 –
25 % CO – 30 % CO2 – 25 % N2 – 5%). A typical
fuel in the second group is referred to as SYNGAS 2,
and has the following composition — (CH4 – 10 %
H2 – 15 % CO – 15 % CO2 – 10 % N2 – 50 %). In

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Acta Polytechnica Vol. 52 No. 3/2012

the rest of this paper these fuels (H2NG0, H2NG15,
SYNGAS 1 and SYNGAS 2) will be used to drive
a Lombardini LWG 702 internal combustion engine,
and the parameters will be evaluated.

2 Lombardini LGW 702
combustion engine

Our workplace has been applying H2NG gas mixtures
(0 to 30 % vol. H2) to drive an LGW 702 internal
combustion engine. This is a two-cylinder gas engine
with electronically controlled richness of the mixture.
The basic characteristics of the LGW 702 engine are
summarized in Table 1.

Before the actual application of the gas mixture
in a combustion engine, it was necessary to make a

simulation analysis to obtain an indicative idea of the
behaviour of the internal combustion engine with a
given fuel mixture. Simulations were performed on
a one-zone model of combustion for the LGW 702
engine, in the Lotus Engine Simulation calculation
program (LES). This program is used for simulating
the operation of the internal combustion engine, and
it is also used as a valuable source of information on
the operational parameters of the LGW 702 internal
combustion engine in reaction to various gas mixtures
that will be experimentally verified step-by-step.

The basic parameters required as input data char-
acterizing a fuel in the LES program are shown in
Table 2.

Figure 1 shows a model of the LGW 702 engine
in the LES program. This model will serve us later
to optimize the combustion engine in terms of per-
formance parameters for various types of fuel blends.

Table 1: Main parameters of the LGW 702 internal combustion engine

Principle of operation Spark ignition

Number of cylinders and their positions 2, in-line

Angle of crank throw [◦] 360

Displacement [cm3] 686

Bore [mm]/Stroke[mm] 75/77.6

Compression ratio [–] 12.5 : 1

Double overhead camshafts, drive OHC, gearing belt

Valve timing
IVO – 18◦ BTDC, IVC – 34◦ ABDC
EVO – 32◦ BBDC, EVC – 32◦ ATDC

Preparation of mixture
External, in a mixer, with electronic regulation of

the air excess ratio, VOILA Plus system

Cooling
By liquid, with forced circulation,

double circular, controlled with a thermostat,
cooler ventilated

Lubrication
Pressure, forced-feed lubrication,

with filtration, oil 1.6 l

Mass without fillings [kg] 66

Table 2: Basic physical-chemical properties of fuel mixtures

Fuel
M H/C ρ r Hu Lt

[kg · kmol−1] [–] [kg · m−3] [J · kg−1 · K−1] [kJ · kg−1] [kg · kg−1]
H2NG0 16.64 3.93 0.705 499.7 48 825 17.00

H2NG15 14.45 4.28 0.613 575.4 50 314 17.36

SYNGAS 1 23.72 2.44 0.969 350.5 11 147 3.67

SYNGAS 2 24.52 2.80 1.002 339.1 6 418 2.11

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Acta Polytechnica Vol. 52 No. 3/2012

Figure 1: Virtual model of the LGW 702 engine in the Lotus Engine Simulation program

Figure 2: Course of the measured and calculated torque Mt, and specific fuel consumption mpe, depending on
the speed n of the LGW 702 engine for H2NG0 and H2NG15 mixtures

Figure 3: Course of the calculated effective efficiency ηe and the fuel consumption MF of the LGW 702 internal
combustion engine for various fuels for a stoichiometric mixture and a full load

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Acta Polytechnica Vol. 52 No. 3/2012

Figure 4: Course of the composition of the exhaust gases, measured behind the catalytic converter, in dependence
on the richness of the mixture, for blends H2NG0 (0 % vol. H2) and H2NG15 (15 % vol. H2) at full load and
at an internal combustion engine speed of 1 800 min−1

3 Results of the simulations
and experiments

Figure 2 shows two basic indicators of the internal
combustion engine (torque and specific fuel consump-
tion), which serve for comparing the simulation and
the experiment. A comparison of the simulations and
the experimental measurements showed that the dif-
ference between the real engine and the virtual model
of the engine was approximately 2 %. The experi-
mental results also showed that the torque of the en-
gine in operation with H2NG15, compared to natural
gas (H2NG0), was on an average 2 % lower, which on
an average meant a decrease of 0.8 N·m. The specific
fuel consumption was on an average 3.3 % lower when
the engine was running on the H2NG15 mixture than
when running on natural gas (H2NG0).

Figure 3 shows a simulation of the effective effi-
ciency and the fuel consumption for the four basic
fuels listed above. The graph shows that the most
effective efficiency was achieved when the engine op-
erated on natural gas, and it was 30 % in the speed
range from 1 800 to 2 000 min−1.

By contrast, the lowest effective efficiency was
achieved when the engine operated on SYNGAS 2
(60 % inert gases), and the efficiency being around
11 % in the speed range from 1 200 to 2 000 min−1.
The mass consumption of the fuel as a stoichiomet-
ric mixture was highest when the engine operated on
the SYNGAS 2 mixture. In comparison with the use
of SYNGAS 1, there was a rise in consumption of
about 48 %. The decrease in the H2NG15 mass fuel
mixture was about 3 % lower than when the engine
operated on natural gas (H2NG0).

Several previously published results have shown
a significant effect of blending hydrogen into natural
gas with the aim to improve the emission parameters
of internal combustion engines. The reason is that
hydrogen blending increases the molar proportion of
H/C, thus reducing the emissions of CHx, CO and
CO2. Figure 4 shows the course of the composition
of the exhaust gases, depending on the air excess ra-
tio for various fuel types (H2NG0 and H2NG15). As
can be seen, there is significant production of car-
bon monoxide CO in the operation of natural gas
(H2NG0) in rich mixtures, where the influence of
oxygen deficiency prevents perfect oxidation of CO
to CO2. Conversely, the production of CO in lean
mixtures is practically zero. The nature and course
of the CO yield is the same when the engine is run-
ning on the H2NG15 mixture (15 % vol. H2).

Complete combustion of hydrocarbon fuels pro-
duces carbon dioxide CO2. It can be seen that the
largest proportion of CO2 is for a slightly lean mix-
ture, with the highest combustion efficiency. From
this value, the proportion of CO2 decreases similarly
as in the rich mixture, which is caused by lack of oxy-
gen to complete the conversion to CO2. The same
situation also arises in the lean mixture, because of
the limited amount of carbon in the fuel. When the
engine runs on the H2NG15 mixture, there is a 9 %
reduction in CO2, on an average, throughout the
course, compared to H2NG0. This is because the
proportion of carbon in the fuel decreases.

Nitrogen oxides NOx, in the case of engine op-
eration on natural gas are formed by oxidation of
nitrogen and oxygen present in the air. Nitrogen and
oxygen oxidize each other at high temperature. As
can be seen, the highest growth occurs for a slightly

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Acta Polytechnica Vol. 52 No. 3/2012

lean mixture that has the highest combustion tem-
perature with a relative abundance of oxygen. With
the gradual transition into leaner areas, the amount
of NOx decreases with lower combustion tempera-
ture. In the area of rich mixtures with a lack of oxy-
gen, there is a decrease in NOx. The course of NOx
formation is similar to the combustion of H2NG15
mixture, but due to the higher combustion temper-
atures, the concentration of NOx increases to about
35 % of the maximum NOx values.

The formation of NOx is closely related to the
proportion of residual oxygen in the exhaust gas. In
operation with H2NG15 mixture, the formation is
lower by about 5 %, than in operation with H2NG0
natural gas. As shown in Figure 4, an increase in
the admixture of hydrogen to natural gas increases
the operating range of an internal combustion en-
gine, mainly in lean mixtures. The addition of 15 %
vol. hydrogen shifts the operating range of an inter-
nal combustion engine from around λ = 1.35 to a
value of λ = 1.5.

4 Conclusion

Mixtures of natural gas and hydrogen have a ma-
jor advantage over other types of fuels for power-
ing internal combustion engines: they produce lower
exhaust emissions, particularly unburned hydrocar-
bons, namely carbon monoxide and carbon dioxide.
However, adding hydrogen to natural gas increases
the amounts of NOx, which can be partly removed
in operation modes with lean mixtures. With an in-
creasing proportion of hydrogen, there is a decrease

in the performance parameters of the internal com-
bustion engine. However, the benefits include oper-
ating the engine on a lean mixture at partial load,
because with added hydrogen the operation range of
a combustion engine working with a lean mixture in-
creases.

Another benefit of our investigation is its contri-
bution to the application of synthesis gas in internal
combustion engines. Synthesis gases have significant
potential for effective utilization of low-energy gases
in co-generation units.

Acknowledgement

This work was supported by the Slovak Re-
search and Development Agency under contract No.
APVV-0270-06 and contract No. APVV-0090-10.

References

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mental study on a spark ignition engine fuelled by
methane-hydrogen mixtures, International Jour-
nal of Hydrogen Energy, 32, 2007, p. 4 279–4 284.

[2] Huang, Z., Bing, L.: Experimental Study on En-
gine Performance and Emissions for an Engine
Fuelled with Natural Gas — Hydrogen Mixtures,
Energy Fuels, 2006, p. 2 131–2 136.

[3] Eichlseder, H., Klell, M.: Wasserstoff in der
Fahrzeugtechnik. Vieweg + Teubner, 2008. ISBN
3834804789.

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